Transient and modulated photoconductivity in microcrystalline silicon

2004 ◽  
Vol 808 ◽  
Author(s):  
R. Brüggemann ◽  
C. Longeaud ◽  
J.P. Kleider
Keyword(s):  
Fermi Level ◽  
Density Of States ◽  
Large Degree ◽  
Dark Conductivity ◽  
Microcrystalline Silicon ◽  
Fermi Level Position ◽  
Transient Photocurrent ◽  
History Of ◽  
Adsorption Of Gases ◽  
Localised States

ABSTRACTWe report on transient and modulated photoconductivity experiments with undoped michrystalline silicon in which access to density-of-states information is limited because the Fermi level results in occupancy of localised states in the energy range which is scanned. Simulation results show that a defect peak will be masked if most of the distribution is occupied because of the Fermi level position and the density-of-states determined from the experimental data is not an image of the true distribution. Another difficulty with obtaining reliable density-of-states distributions in microcrystalline silicon is the metastability of samples with respect ot adsorption of gases. If dark-conductivity changes are large upon heat treatment in vacuum, the modulated and transient photocurrent response are also affected to a large degree and the density-of-states profiles apart form being influenced by the Fermi level position thus also depend on the thermal history of the sample.

Metastable Changes in the Photoconductive Properties of Microcrystalline Silicon Upon Heat Treatment

2005 ◽  
Vol 862 ◽  
Author(s):  
R. Brüggemann
Keyword(s):  
Heat Treatment ◽  
Fermi Level ◽  
Carrier Mobility ◽  
Minority Carrier ◽  
Dark Conductivity ◽  
Effective Density ◽  
Ambient Conditions ◽  
Microcrystalline Silicon ◽  
Treatment Procedures ◽  
Minority Carrier Mobility

AbstractWe demonstrate that metastable changes or instabilities in the dark conductivity of microcrystalline silicon upon heat treatment and ambient conditions, which have been reported in the literature, are accompanied by changes in the photoconductivity or the majority-carrier mobility-lifetime product. The minority-carrier mobility-lifetime product and sub-gap absorption appear to be much less affected by different heat treatment procedures and ambient conditions. The observations can be related to Fermi-level induced change in defect occupancy by which the effective density of recombination centres is reduced for electrons but remains the same for holes. Minority carrier properties seem to be better suited as an indicator for sample quality and for comparison of microcrystalline silicon samples from different laboratories.

The Meyer-Neldel Rule in Conductivity of Microcrystalline Silicon

2002 ◽  
Vol 715 ◽  
Author(s):  
Sanjay K. Ram ◽  
Satyendra Kumar ◽  
P. Rocai Cabarrocas
Keyword(s):  
Activation Energy ◽  
Grain Boundary ◽  
Film Thickness ◽  
Fermi Level ◽  
Carrier Transport ◽  
Dark Conductivity ◽  
Localized States ◽  
Microcrystalline Silicon ◽  
Thermally Activated ◽  
Density Of Localized States

AbstractThe dark conductivity (σd) has been measured from 300 to 440K on undoped hydrogenated microcrystalline silicon (μc-Si:H) films having different thicknesses. The carrier transport is found to be thermally activated with single activation energy (Ea) in all the samples. The Ea increases as the film thickness decreases. At the same time logarithmic of dark conductivity prefactor (σo) is found to follow a linear relation with activation energy, known as the Meyer-Neldel rule (MNR). Results are explained in terms of increased degree of disorder in thinner samples. Thus change in Ea with the film thickness is directly related to the density of localized states at the Fermi level in grain boundary (GB). Therefore varying the film thickness and, hence, the exponential density of states induces a statistical shift of Fermi level which gives rise to the observed MNR.

Transport Path in Hydrogenated Microcrystalline Silicon

2002 ◽  
Vol 715 ◽  
Author(s):  
N. Wyrsch ◽  
C. Droz ◽  
L. Feitknecht ◽  
J. Spitznagel ◽  
A. Shah
Keyword(s):  
Raman Spectroscopy ◽  
Volume Fraction ◽  
Conductivity Measurement ◽  
Dark Conductivity ◽  
Transition Regime ◽  
Conductivity Data ◽  
Crystalline Volume Fraction ◽  
Microcrystalline Silicon ◽  
Crystalline Fraction ◽  
Transport Path

AbstractUndoped microcrystalline silicon samples deposited in the transition regime between amorphous and microcrystalline growth have been investigated by dark conductivity measurement and Raman spectroscopy. From the latter, a semi-quantitative crystalline volume fraction Xc of the sample was deduced and correlated with dark conductivity data in order to reveal possible percolation controlled transport. No threshold was observed around the critical crystalline fraction value Xc of 33%, as reported previously, but a threshold in conductivity data was found at Xc≈50%. This threshold is interpreted here speculatively as being the result of postoxidation, and not constituting an actual percolation threshold.

High Temperature n- and p-type Doped Microcrystalline Silicon Layers Grown by VHF PECVD Layer-by-Layer Deposition

2003 ◽  
Vol 762 ◽  
Author(s):  
A. Gordijn ◽  
J.K. Rath ◽  
R.E.I. Schropp
Keyword(s):  
Activation Energy ◽  
High Temperature ◽  
High Temperatures ◽  
Continuous Wave ◽  
Hydrogen Plasma ◽  
Silicon Layer ◽  
Dark Conductivity ◽  
High Deposition Rate ◽  
Layer By Layer ◽  
Microcrystalline Silicon

AbstractDue to the high temperatures used for high deposition rate microcrystalline (μc-Si:H) and polycrystalline silicon, there is a need for compact and temperature-stable doped layers. In this study we report on films grown by the layer-by-layer method (LbL) using VHF PECVD. Growth of an amorphous silicon layer is alternated by a hydrogen plasma treatment. In LbL, the surface reactions are separated time-wise from the nucleation in the bulk. We observed that it is possible to incorporate dopant atoms in the layer, without disturbing the nucleation. Even at high substrate temperatures (up to 400°C) doped layers can be made microcrystalline. At these temperatures, in the continuous wave case, crystallinity is hindered, which is generally attributed to the out-diffusion of hydrogen from the surface and the presence of impurities (dopants).We observe that the parameter window for the treatment time for p-layers is smaller compared to n-layers. Moreover we observe that for high temperatures, the nucleation of p-layers is more adversely affected than for n-layers. Thin, doped layers have been structurally, optically and electrically characterized. The best n-layer made at 400°C, with a thickness of only 31 nm, had an activation energy of 0.056 eV and a dark conductivity of 2.7 S/cm, while the best p-layer made at 350°C, with a thickness of 29 nm, had an activation energy of 0.11 V and a dark conductivity of 0.1 S/cm. The suitability of these high temperature n-layers has been demonstrated in an n-i-p microcrystalline silicon solar cell with an unoptimized μc-Si:H i-layer deposited at 250°C and without buffer. The Voc of the cell is 0.48 V and the fill factor is 70 %.

scholarly journals Investigation of single-domain Au silicide nanowires on Si(110) formed for Au coverages in the monolayer regime

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Stephan Appelfeller
Keyword(s):  
Fermi Level ◽  
Surface Structure ◽  
Density Of States ◽  
The Self ◽  
Single Domain ◽  
Photoemission Spectroscopy ◽  
Annealing Temperatures ◽  
Self Organized ◽  
Scanning Tunnelling ◽  
Tunnelling Microscopy

AbstractThe self-organized formation of single domain Au silicide nanowires is observed on Si(110). These nanowires are analysed using scanning tunnelling microscopy (STM) and spectroscopy (STS) as well as photoemission spectroscopy (PES). Core-level PES is utilised to confirm the formation of Au silicide and establish its presence as the top most surface structure, i.e., the nanowires. The growth of the Au silicide nanowires and their dimensions are studied by STM. They form for Au coverages of about 1 monolayer and are characterized by widths of about 2 to 3 nm and heights below 1 nm while reaching lengths exceeding 500 nm when choosing appropriate annealing temperatures. Valence band PES and STS indicate a small but finite density of states at the Fermi level typical for compound metals.

Photosensitive tunneling in superconductivity

1970 ◽  
Vol 48 (5) ◽  
pp. 630-631 ◽  
Author(s):  
V. Radhakrishnan
Keyword(s):  
Fermi Level ◽  
Density Of States ◽  
Tunneling Current ◽  
Theoretical Treatment ◽  
Photoconductive Property

Theoretical treatment of the model proposed by Giaever for his experiment on the photosensitive tunneling in superconductors is examined. New relations are derived which connect the photoconductive property of the barrier and the tunneling current. These relations are helpful to check the model and to determine the density of states for the trapped holes at the hole Fermi level.

scholarly journals Were they really laughed at? That much? Gelotophobes and their history of perceived derisibility

2009 ◽  
Vol 22 (1-2) ◽  
Author(s):  
René T. Proyer ◽  
Christian F. Hempelmann ◽  
Willibald Ruch
Keyword(s):  
Empirical Study ◽  
Large Degree ◽  
Time Span ◽  
Corpus Study ◽  
The Past ◽  
History Of ◽  
University Of Zurich

AbstractThe List of Derisible Situations (LDS; Proyer, Hempelmann and Ruch, List of Derisible Situations (LDS), University of Zurich, 2008) consists of 102 different occasions for being laughed at. They were retrieved in a corpus study and compiled into the LDS. Based on this list, information on the frequency and the intensity with which people recall being laughed at during a given time-span (12 months in this study) can be collected. An empirical study (N = 114) examined the relations between the LDS and the fear of being laughed at (gelotophobia), the joy of being laughed at (gelotophilia), and the joy of laughing at others (katagelasticism; Ruch and Proyer this issue). More than 92% of the participants recalled having been laughed at at least once over the past 12 months. Highest scores were found for experiencing an embarrassing situation, chauvinism of others or being laughed at for doing something awkward or clumsy. Gelotophobia, gelotophilia, and katagelasticism were related about equally to the recalled frequency of events of being laughed at (with the lowest relation to katagelasticism). Gelotophobia, gelotophilia, and katagelasticism yielded a distinct and plausible pattern of correlations to the frequency of events of being laughed at. Gelotophobes recalled the situations of being laughed at with a higher intensity than others. Thus, the fear of being laughed at exists to a large degree independently from actual experiences of being laughed at, but is related to a higher intensity with which these events are experienced.

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